Classic Projects - The Statue of Liberty

We look at the facts and figures that add up to one of the greatest engineering icons of all time.

Liberty was a centennial gift from France to America to commemorate the anniversary of the Declaration of Independence. But in terms of delivery it was an embarrassment, being a decade late.

Instantly recognisable, Liberty – or to use her correct name La Liberté éclairant le monde – traces her roots to one of the Seven Wonders of the Ancient World, the Lighthouse of Alexandria. The statue keeps watch over New York Harbour and for more than a century has been a symbol of welcome to immigrants seeking a new life in the New World. The American poet Emma Lazarus wrote Liberty's immortal words: 'Give me your tired, your poor, your huddled masses yearning to breathe free.'

Liberty combines the artistic vision of sculptor Frédéric Bartholdi and the structural engineering genius of Gustave Eiffel. Bartholdi came up with the concept of the statue, but the sculptor realised he needed the help of an engineer to address structural issues. Eiffel's design was a massive iron pylon, supporting a secondary skeletal framework that in turn supports the statue's copper skin.

Meanwhile, across the pond fundraising was at a standstill and remained so until newspaperman Joseph Pulitzer stepped in and opened up a public subscription via his editorial pages.

The idea was that the French would supply the statue itself while the Americans would take care of the pedestal and assembly. Both got off to inauspicious starts, hampered by funding problems, protests from French monarchists and objectors to America's refusal to assist France in the Prussian war. But work went ahead in fits and starts with body parts exhibited at the Independence Centenary exhibition in Philadelphia – with the head being shown at the Paris World's Fair 1878 – despite the overall design of the piece being far from finalised.

Eiffel's design is one of the earliest examples of curtain-wall construction, in which the exterior of the structure is not load-bearing,'but supported by an interior framework. The exterior envelope was composed of brass plaques, formed by hammering them in hard-wood moulds made from plaster models. These plaques were then soldered and riveted together.

Bartholdi then prefabricated the figure in Paris by moulding sheets of copper over a steel framework. The designers originally planned to assemble the copper skin onto the armature extensions on site, concurrent with the construction of the pedestal. But the plan proved too ambitious and eventually Liberty was put together in France, before being taken apart and shipped to the States. The statue was reduced to 350 individual pieces and packed in 214 crates. It was re-erected four months later on Bedloe's Island (now Liberty Island).

In 1982, Liberty underwent extensive restoration in advance of the 1986 centennial. Engineers found that the right arm had been attached wrongly and was posing a severe risk of structural failure. The head was also found to have been placed off centre. More than 2 per cent of the copper needed replacing with extensive cleaning required for the remainder. The entire restoration project cost more that $350m.

In 1984 the Statue of Liberty was inscribed on the UNESCO world heritage list, described as 'a masterpiece of the human spirit' and 'a bridge between art and engineering'. After the 9/11 terror attacks in New York in 2001 the statue was closed to the public, gradually reopening with limited access to the crown gallery. Later this year Liberty will be closed to install a second staircase.